BCW: Buffer-Controlled Writes to HDDs for SSD-HDD Hybrid Storage Server
summary
Claims HDDs can serve many writes at μs-level by exploiting periodic buffered-write phases; experiments on five production HDDs show 35–180μs fast-phase writes interspersed with ~12ms spikes, with fast/mid phase lengths about 16MB/8MB. A prediction model plus Buffer-Controlled Write (BCW) and a Mixed IO Scheduler (MIOS) are implemented and evaluated on Pangu workloads; MIOS cuts SSD write volume up to 93% and reduces average and 99th‑percentile latencies by ~65% and ~85%.
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